Book/Dissertation / PhD Thesis

FZJ-2017-08538

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Mechanismen des Hochtemperaturrisswachstums in einem ferritischen Stahl an Luft und in Wasserdampf

Fischer, T. (Corresponding author)FZJ*

2018
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag Jülich
ISBN: 978-3-95806-326-6

Please use a persistent id in citations: http://hdl.handle.net/2128/18897

Abstract: Nowadays the requirements on conventional power plants have fundamentally changed. Du eto an increase of renewable energies proportion, e. g. wind power and photovoltaics, which cannot supply energy constantly, modern power plants must be able to be operated flexibly in order to compensate the fluctuation in residual load. As a result of the rising number of startup and shutdown processes and thus temperature and internal pressure fluctuations, the materialis strongly stressed. As a result of increasing alternating load, the fatigue damage becomes more and more important, while the influence of the creep damage caused by ever shorter hold time at high operating temperatures decreases. Owing to the increasing cyclic stress, the main focus is on thick-walled power plant components in feedwater and fresh steam systems, for e. g. spheroidal forgings, fittings, collectors, pumps and turbine bypass valves (TBV). Within the scope of the Federal Ministry for Economic Affairs and Energy joint research project THERRI (determination of characteristic parameters for the evaluation of thermal fatigue crack growth in power plants), two TBVs were provided after 21 years of service by Kraftwerks- und Netzgesellschaft (KNG) mbH for fracture mechanics experiments. The material of the TBV is X20CrMoV12-1, a widespread standard 9 - 12 % Cr ferritic/martensitic steel in the power industry. In the present work, the influence of frequency, hold time and atmosphere at maximum load on crack propagation in a temperature range of 300 °C - 600 °C, which is relevant for the load-flexible power plant operation, was investigated. For this temperature range, data is scarce in the literature. Furthermore, the combination of temperature/frequency/hold time was identified, where fatigue-dominated crack growth devolves to creep fatigue interaction. To characterize the microstructural damage mechanisms and, extensive light and electron microscopy studies were performed. Extensive fracture mechanics studies have shown that during the hold time test, larger crack growth rates per cycle occur than in the fatigue crack growth test. In comparison to pure cyclic loading, crack propagation starts at significant higher $\Delta$K-values, which is caused bythe hold time at maximum load. In the fatigue crack growth test, the crack growth rate increases slightly with decreasing frequency. Because of a dependence of steam atmosphere effects on frequency (or hold time)and temperature, pure atmosphere effects cannot be observed on crack growth or on the start of crack growth.

Note: RWTH Aachen, Diss., 2017

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Contributing Institute(s):

1. Werkstoffstruktur und -eigenschaften (IEK-2)

Research Program(s):

1. 111 - Efficient and Flexible Power Plants (POF3-111) (POF3-111)
2. HITEC - Helmholtz Interdisciplinary Doctoral Training in Energy and Climate Research (HITEC) (HITEC-20170406) (HITEC-20170406)

Appears in the scientific report 2017

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